The invention relates to a device for connecting a tool head, which has a tool shank, to a clamping shank, which has a seat for the tool shank and is preferably arranged at the end side on a machine spindle, with the aid of a clamping mechanism which has at least two clamping elements, which are arranged at an angular distance from one another and, in their clamping position, connect the tool shank and the clamping shank to one another in a force-fitting manner, and an actuating mechanism for the limited displacement of the clamping elements between a release position and a clamping position.
The clamping elements which can be adjusted using the actuating mechanism are used to generate a pressure between planar surfaces of the parts which are to be coupled to one another. In a known device of this type, the claw-like or clip-like clamping elements, at one end, are fitted into the seat of the clamping shank, while at the other end they extend into the interior of the tool shank, which is of hollow design. They can be supported, by means of in each case two clamping shoulders, which are arranged at an axial distance from one another and face toward one another, on clamping surfaces which are arranged in the interior of the clamping shank and of the hollow tool shank and face away from one another, and can be adjusted between a release position and a clamping position by means of the actuating mechanism. One frequently encountered drawback of the known device is that during the clamping operation it is necessary to overcome relatively high frictional forces and spring forces which act in the opposite direction to that of achieving a high clamping force between the parts which are to be coupled. A further drawback of the known coupling device of this type consists in the relatively complicated mechanical structure, which frequently comprises filigree individual parts, of the clamping mechanism, which particularly with small sizes leads to strength and assembly problems.
In view of the above, the invention is based on the object of developing a connecting device of the type mentioned in the introduction which is easy to produce and assemble.
The combinations of features given in patent claims 1, 33, 38, 44, 60, 75 and 82 are proposed in order to achieve this object. Advantageous configurations and refinements of the invention will emerge from the dependent claims.
To achieve this object, according to the invention, it is primarily proposed that in each case one piston-like centering element engage over the clamping insert at its end-side ends, and that the centering elements be rigidly connected to one another by means of axially parallel webs, so as to form a centering cage which engages over the clamping mechanism with axial play, and in each case engage in one axially central, preferably cylindrical recess in the region of the base of the clamping shank and the tool shank, which is preferably designed as a hollow shank, leaving clear an axial space.
The centering cage is expediently designed as an ejector element which, under the action of the actuating mechanism when the clamping mechanism is being released, separates the tool shank from the clamping shank in the axial direction. In a preferred configuration of the invention, a fluid pressure can be applied to the centering cage at its centering element on the clamping shank side, via the free space, in the direction of the hollow shank. The webs may be of hollow design, so as to form in each case one coolant pipe, while the piston-like centering elements have inlet openings and outlet openings which are in communication with the coolant pipes. The clamping mechanism with the actuating mechanism, on the one hand, and the centering cage, which is designed as a coolant bridge, on the other hand, in the assembled state form a structural unit which during assembly can be fitted into the clamping shank by one simple action, and can be locked therein, for example by means of the locking bolt.
Advantageously, the centering element on the clamping shank side has at least one inlet opening which is oriented in an axially parallel direction and can be sealed by means of a radial seal inside the associated recess. To avoid baffle surfaces in the feed line, which could cause the coolant fluid to become segregated, it is advantageous if at least one inlet opening is connected to a central passage on the clamping shank side via an inclined, edgeless inlet passage. Such an arrangement is advantageous in particular for minimal-quantity lubrication, in which a carrier gas laden with oil particles (an aerosol) is used as the coolant fluid instead of a liquid coolant.
The centering element on the hollow shank side advantageously has a central outlet opening which is preferably in communication with the coolant pipes via inclined, edgeless outlet passages, and can be sealed inside the associated recess by a seal which surrounds the outlet opening on the outside. To prevent depositions and pressure drops in the flowing cooling fluid when minimal-quantity lubrication is used, it is proposed, according to a preferred configuration of the invention, for the central passage on the clamping shank side, the inlet passages, the coolant pipes, the outlet passages and the central outlet opening to have a cross section of flow which is substantially constant or, in sections, increases or decreases continuously.
According to a preferred configuration of the invention, the seal on the hollow shank side is designed as an axial seal. This arrangement has the advantage that the seal cannot be damaged during a tool change. It is also possible to provide a lip seal at that location, the sealing lip of which can be pressed against a base surface or a lateral surface of the recess on the hollow shank side under the action of the coolant pressure. If pressure is therefore applied to the tool head by means of coolant via a passage on the clamping shank side after the coupling operation, the centering cage is displaced, under the action of the coolant, toward the tool head, so that the centering element on the hollow shank side comes into contact with its seal. A further improvement in this respect is achieved by the fact that a spring member which presses the centering cage gently toward the tool head is arranged between the clamping shank and the centering cage. The spring member may in this case be designed as a helical compression spring which is arranged in a cylindrical recess in the clamping shank and is gently preloaded between the clamping shank and the centering element on the clamping shank side. The gentle preloading is to be selected in such a way that the centering cage is reliably displaced toward the tool head while, nevertheless, it does not present any significant resistance during the clamping operation.
The centering element on the clamping shank side may have an axially central pocket for holding ends, on the clamping shank side, of the clamping elements, which ends project axially beyond the clamping insert in such a manner that they float in the axial and radial directions.
A significant advantage of the clamping insert with split clamping elements consists in the greater ease of assembly and dismantling with a prefabricated centering cage. The clamping elements are expediently fitted releasably into the prefabricated centering cage.
To make it easier to introduce the hollow shank into the hollow-shank seat of the clamping shank, it is proposed, according to a preferred configuration of the invention, for a spring element which preloads the centering cage in the direction of the clamping shank to be arranged between the clamping insert and the centering cage. The spring force of the spring element is to be selected in such a way that the forces acting on the centering cage under the action of the coolant pressure are able to overcome the spring force. The spring element may at the same time be designed as a centering member for the clamping insert. In particular, the spring element may be designed as a helical compression spring, one end of which engages in pitch-circle recesses, which are open toward the clamping shank side, in the clamping elements, and the other end of which is supported on the centering element on the clamping shank side. To achieve a balance, it is advantageous if the clamping elements of the clamping insert are pressed radially outward or inward via the spring element, so that they are not exposed to any free play in the radial direction. This can be achieved by the fact that the clamping elements each have an inclined support shoulder, which faces inward or outward on one side, for the spring element, which is preferably designed as a helical compression spring. These measures ensure that, due to the symmetrical design, the principal axis of inertia coincides with the axis of rotation, which is advantageous in particular for high-speed machining.
Alternatively, the spring element may be designed as a compression spring, one end of which is supported on the intermediate member and the other end of which is supported on the centering element on the clamping shank side. The axially projecting ends, on the clamping shank side, of the clamping elements may form an axially central seat for an intermediate member which is designed as a roller or ball. Expediently, in the clamping position they complement one another to form a conical outer surface which tapers toward the clamping shank, and in the release position they complement one another to form a cylindrical outer surface which advantageously vertically adjoins the end faces, on the clamping shank side and which face radially outward, of the clamping elements.
A further aspect according to the invention consists in the fact that, by means of an additional spring force which acts on the clamping elements in the clamping direction of the actuating mechanism, it is possible to achieve a high clamping force even with relatively low forces acting on the actuating element. Advantageously, in this case the clamping elements, in their release position, are preloaded in the clamping direction under the action of the spring force. The spring force may decrease in the clamping direction, so that the clamping elements, in their clamping position, are substantially free of preloading with respect to the spring force. As a result, in the clamping position of the clamping elements, it is also possible to minimize the frictional forces inside the clamping mechanism and the actuating mechanism, which otherwise counteract the clamping force.
In a preferred configuration of the invention, two clamping elements, which lie opposite one another in the clamping direction, are connected to one another, preferably integrally, via a spring element which, in the release position of the actuating mechanism, is preloaded in the clamping direction the spring element advantageously being completely or virtually stress-free in the clamping position of the actuating mechanism.
In a further preferred or alternative configuration of the invention, two clamping elements or clamping-element pairs, which lie radially opposite one another, are integrally connected to one another, at their end on the clamping shank side, via a flexural joint, so as to form a single-piece clamping insert, and can be radially bent with respect to one another about the bending axis of the flexural joint by means of the actuating mechanism. In this arrangement, the flexural joint of the clamping insert is advantageously in the form of a U-shaped spring loop which projects axially beyond the ends, on the clamping shank side, of the clamping elements or the clamping-element pairs.
To enable the clamping forces to be distributed uniformly over the circumference of the hollow shank and the clamping shank, it is proposed, according to a preferred configuration of the invention, for the clamping-element pairs, at their ends on the clamping shank side, to have clamping elements which are integrally connected to one another in pairs via a second flexural joint, which is oriented transversely with respect to the first flexural joint, and can be bent with respect to one another about their bending axis with the aid of the actuating mechanism. In the clamping position of the clamping elements, at least the first flexural joint is free from preloading and in the clamping position is spring-preloaded.
As an alternative, it is proposed, according to the invention, that two clamping elements or clamping-element pairs, which lie radially opposite one another, are designed as separate parts which bear directly or indirectly, via an intermediate member, against one another so as to form a clamping insert at their ends on the clamping shank side or at an axial distance therefrom, and, via the actuating mechanism, can be pivoted substantially radially with respect to one another about the tilting axis formed by the contact point.
In this case too, it is advantageous if the clamping-element pairs, at their ends on the clamping shank side, have clamping elements which are integrally connected to one another in pairs via a flexural joint, which is oriented transversely with respect to the tilting axis, and can be bent with respect to one another about their bending axis with the aid of the actuating mechanism. Advantageously, the ends, on the clamping shank side, of the clamping elements or clamping-element pairs are of convex design in the region of the contact point. The intermediate member is advantageously designed as a roller or ball which is fitted loosely between the ends on the clamping shank side. To avoid axial displacements of the clamping elements or clamping-element pairs with respect to one another, the ends on the clamping element side may be held together by means of a spring, for example by means of a spring washer or a spring clip.
In a preferred or alternative configuration of the invention, the actuating mechanism has two pressure-exerting pieces, which can be fitted into in each case one recess, which is open on the end side and radially inward, in the clamping elements or clamping-element pairs which lie radially opposite one another, and at least one screw element for adjusting the distance between the pressure-exerting pieces. The screw element may be designed as a differential screw, the threaded parts of which engage in oppositely directed screw threads, which are flush with one another and are radially oriented, of the pressure-exerting pieces.
The pressure-exerting pieces may in principle also be integrally connected to one another via a flexural joint which is preferably designed as a spring loop. In this case, the screw element is expediently designed as a threaded bolt which engages through an internal screw thread of one of the pressure-exerting pieces and the end face of which bears against an abutment of the other pressure-exerting piece. Advantageously, a second threaded bolt, the end face of which forms the abutment for the first threaded bolt, engages through an internal screw thread of the other pressure-exerting piece.
In order, during the clamping operation, additionally to achieve a spreading action between the clamping elements of each clamping-element pair, the pressure-exerting pieces advantageously have a profile which is wedge-shaped or convex toward the adjacent clamping-element pair. To improve the spreading action, the convex or wedge-shaped profile of the pressure-exerting pieces may be divided into an in-feed slope which is relatively shallow in the in-feed direction and an adjoining relatively steep clamping slope.
According to a preferred configuration of the invention, the pressure-exerting pieces have a pressure-exerting surface which is partially cylindrical toward the adjacent clamping element and by means of which they can roll along the preferably planar stop surface of the clamping element during the clamping operation. In order to distribute the pressure over a larger surface area in the clamped state, it is advantageous if the pressure-exerting surface has a planar apex surface which adjoins the partially. cylindrical section and, in the clamped position of the pressure-exerting pieces, bears against the bearing surface with surface-to-surface contact. A further improvement in this respect is achieved by the fact that the internal screw thread of the pressure-exerting pieces and the external screw thread of the screw element have a clearance which permits tolerance compensation.
In an advantageous configuration of the invention, the clamping elements and/or the pressure-exerting pieces are surface-hardened or have a wear-resistant and/or friction-reducing surface coating, which may be formed either as a layer of hard material, for example of metal, or as a layer of soft material, for example of graphite or polytetrafluoroethylene.
The clamping elements of each clamping-element pair are advantageously separated from one another by in each case one axial gap which preferably continues all the way to the second flexural joint. This at the same time, ensures that an engagement piece which is arranged on the screw element or on the threaded spindle is radially accessible to a screwdriver through the axial gaps. To provide access f or the screwdriver to the actuating mechanism, it is additionally possible for the clamping shank and the hollow shank to have apertures which are flush with one another.
To enable the clamping elements or clamping-element pairs to be moved out of their clamping position into the preloaded release position, it is proposed, according to a preferred configuration of the invention, for the pressure-exerting pieces each to have a driver cam which bears against a radially outwardly facing stop surface of the associated clamping elements or clamping-element pairs and drives the latter with it during actuation toward the release position.
In a further advantageous configuration of the invention, the clamping surfaces on the clamping shank side and the associated clamping shoulders of the clamping elements are oriented substantially in a radial plane, while the clamping surfaces on the hollow shank side and the associated clamping shoulders of the clamping elements are designed as inclined or cone surfaces which diverge radially outward with respect to the clamping shoulders and surfaces on the clamping shank side. To achieve the most uniform possible clamping between hollow shank and clamping shank over the circumference, it is advantageous if the clamping shoulders of the clamping elements of each clamping-element pair include a central angle, with respect to the clamping shank axis, of from 30xc2x0 to 120xc2x0, preferably 50xc2x0 to 90xc2x0, with one another.
The clamping shoulders, on the hollow shank side, of the clamping elements are delimited in the circumferential direction by substantially radially oriented delimiting edges and in the radial direction by a delimiting edge which is oriented substantially in the circumferential direction. To avoid local pressure peaks in the area of the clamping shoulders during the clamping operation, taking into account the given dimensional tolerances, it is proposed, according to a preferred configuration of the invention, for at least one of the delimiting edges to be convexly rounded or beveled.
Particularly simple assembly of the clamping insert is achieved by the fact that the clamping insert, by way of its clamping shoulders on the clamping shank side, can be locked to the clamping shank in the manner of a bayonet closure and, in the locking position, can be secured against rotation in a form-fitting manner. To prevent rotation, the clamping insert may be fixed in its locked position by means of a locking bolt which penetrates through the clamping surface of the clamping shank in an axially parallel direction and engages in a form-fitting manner in a recess, which is open at the radial edge, in one of the clamping elements or clamping-element pairs. Optionally, the clamping insert may be fitted into the clamping shank rotated through 180xc2x0 and locked therein.
According to a preferred configuration of the invention, the hollow shank has an outer surface which tapers conically toward its free end, and the clamping shank has a seat of corresponding conicity. The clamping is expediently effected by the fact that the hollow shank is delimited by an annular shoulder which, in the clamping position of the clamping elements, can be pressed against an annular planar surface of the clamping shank.
Since the conical hollow shank and the conical seat are connected to one another in a self-locking manner in the clamped state, an ejector mechanism is additionally required for a tool change. Therefore, in a preferred configuration of the invention, the pressure-exerting pieces, on their mutually facing sides, delimit a gap into which an ejector wedge, which projects on the hollow shank side, preferably at the centering element on the hollow shank side, and can be subjected to an axial force under the action of the pressure-exerting pieces, engages. Expediently, the gap edges, which face toward the ejector wedge, of the pressure-exerting piece are beveled in the shape of a wedge.
According to a further preferred or alternative configuration of the invention, there is a closure ring which engages around the clamping shank on the outside, can be sealed with respect to the clamping shank at its two edges and can be displaced in the axial direction to a limited extent with respect to the clamping shank, between a limit position in which it closes off the apertures and a limit position in which it opens the apertures. For this purpose, the clamping shank, in the region of the apertures, has an annular turned groove, which is adjoined, via in each case one annular step, by a run-up area of larger diameter toward the end side of the clamping shank and by a guide area of larger diameter toward the root of the clamping shank, while the closure ring has in each case one sealing ring which in the annular turned groove and in the guide area bears against the outer surface of the clamping shank. Advantageously, in the closed position of the closure ring, at least one of the sealing rings can be latched into an annular latching indentation in the clamping shank.
According to a further preferred or alternative configuration of the invention, the hollow shank, at its free end, has at least one groove for a driver on the clamping shank side to engage in, while the clamping shank has at least one bore, which is laterally offset with respect to an axial plane, for holding a bolt, which engages in the groove or in a recess in the hollow shank, eliminates the play of the driver in the groove in one direction of rotation of the clamping shank, and is of flexurally elastic design. The bore is advantageously designed as a threaded bore for receiving the bending bolt which has a corresponding screw thread. The bending bolt advantageously has a threaded section, a bending section and a driver section which is thickened in the manner of a hammer at the free end of the bending section. By means of the bending bolt according to the invention, the play between the groove and the driver is eliminated on one side in the direction of loading, the driver bearing against the groove flank via which the torque which results from the principle cutting force is absorbed. To enable the clamping device to be used for both anticlockwise and clockwise tools, it is advantageous if two holes, which are arranged mirror-symmetrically with respect to the axial plane, are arranged in the clamping shank for optionally holding a bending bolt.